A sector forming a part of a camera shutter is generally a mechanical element which is actuated by rotating a motor to define an exposure quantity and an aperture diameter. As a consequence, if the rotation of the motor fluctuates due to a change in battery power, the exposure quantity and aperture diameter cannot be defined properly, and synchronized operation of a strobe light cannot be attained, thereby resulting in inferior photography.
According to Japanese Laid-Open Patent Document No. 61-163027 "Speed Control Device of Camera Shutter Driving Motor", the shutter closing time relating to an exposure quantity E.sub.V is stored in a memory circuit in the form of data for the control of motor speed or data for the control of the width of driving pulses to be sent to a motor. As soon as the operating speed of a sector is detected, the width of the driving pulses is determined as a function of the data stored in the memory circuit. In order to detect the operating speed of the sector, an opening is formed in the sector such that a light beam traveling between light emitting and light receiving elements of a photo-interruptor signal output means is intercepted by the leading edge o passed through the opening of the sector. In Japanese Laid-Open Patent Document No. 61-163027 "Speed Control Device of Camera Shutter Driving Motor", as well as in Japanese Laid-Open Patent Document No. 62-194239, however, which disclose a photo-interruptor means actuated by a sector, although the shutter will be reliably actuated, its malfunction cannot be detected.